1. Field of the Invention
The present invention pertains to sporting ball throwing machines and is specifically concerned with orienting attachments to such machines, which provide for spinning the balls and projecting them in predetermined directions. Such attachments are usually installed at the ball outlet from a ball throwing machine: in a pneumatic ball throwing machine, at the end of its barrel, and in a mechanical one, on its housing in the ball flow path. The invention may be used to the best advantage in tennis or soccer ball throwing machines.
2. Description of the Prior Art
An important problem encountered by designers in developing ball spinning devices for ball throwing machines, in particular for tennis ones, is the provision of such an orienting attachment which would only insignificantly slow down the velocity of balls at the outlet from the ball throwing machine while not abrading them.
Despite the well-known attempts to solve the problem, it still remains to be solved adequately.
Thus, in practice, for spinning the balls, use is made of a simple device which is a strip of friction material, such as rubber, attached in the ball throwing machine to the inner surface of the barrel along the axis thereof in the ball outlet zone, whereas the remaining (i.e. free from the strip) inner surface of the barrel in the ball emergence zone has, on the contrary, an antifriction coating. The difference in the frictional forces acting upon diametrically opposite portions of the ball moving through the barrel gives rise to a torque which imparts to the ball the required spin in the flight.
This device suffers from the following disadvantages: an intense abrasive wear of balls because of their friction against the rubber strip and a low ball ejection velocity because of a loss of its energy resulting from friction against the same strip and the barrel of the ball throwing machine.
There is also known in the art an orienting attachment for a ball throwing machine, comprising a coupling unit to be secured to the machine and a ball deflector hinged to the unit (refer to the Specification ot the USSR Inventor's Certificate No. 490,476, Int. Cl.sup.3. A 63B 69/40). In this attachment, the coupling unit is a hollow cylindrical body and the ball deflector has the form of a double-arm lever mounted on the body, one arm of the lever carrying a flat or channeled deflecting shelf, and the other arm being pressed against said body by a screw whereon a spring is placed. The degree of spinning of a ball ejected from the machine is controlled by varying the force of compression of said spring with the aid of the screw. In this attachment, the spinning degree is greater the longer the ball interacts with the deflecting shelf. For this reason, the deflecting shelf has a friction facing which lengthens the duration of the interaction.
An advantage of such an attachment lies in the possibility of positioning the deflecting shelf at an angle to the axis of the ball throwing machine, makes it possible, firstly, to increase the frictional force at the place of interaction between the ball and the shelf and hence to increase to a certain degree the extent of the ball spin and, secondly, to shorten the length of the sliding of the ball over the shelf and thereby somewhat to diminish the abrasive wear of balls.
Inasmuch, as the ball sliding friction in this attachment is still considerable, the abrasive wear of balls remains as well considerable while their velocity drops significantly. It should also be noted that the above-described attachment calls for a frequent manual adjustment and therefore is unsuitable for use in an automated training system, such as in tennis robots, where changing the intensity of the spin and the position of the ball rotation axis in the space should be provided in the course of operation of the ball throwing machine, in particular, after every hit.